Coating composition a non-porous moisture-permeable coating layer or film of a hydrophilic polyurethane resin

ABSTRACT

A coating composition for forming a substantially non-porous moisture-permeable coating layer or film of a hydrophilic polyurethane resin, which comprises a polyol combination and a polyisocyanate compound, or a prepolymer or polyurethane resin obtained by reacting them, said polyol combination comprising: 
     (a) from about 50 to about 98% by weight of a polyoxyethylene polyol having an oxyethylene group content of from about 50 to about 90% by weight, a hydroxyl valve of from about 15 to about 60 and at least 3 hydroxyl groups; and 
     (b) from about 2 to about 50% by weight of a diol having a molecular weight of from about 62 to about 2,000 which may contain oxyethylene groups; 
     provided that the molar equivalent ratio of the component (b) to the component (a) is from about 0.2 to about 5, and the total oxyethylene group content in the components (a) and (b) is at least about 70% by weight.

This application is a continuation of application Ser. No. 06/903,964,filed on Sept. 5, 1986, now abandoned.

The present invention relates to a coating composition for forming amoisture-permeable coating layer or film of a polyurethane resin.

It is known to produce a moisture-permeable material suitable for usee.g. as a material for clothing by forming a substantially non-porouslayer of a hydrophilic polyurethane resin on a porous substrate such ascloth. This hydrophilic polyurethane resin layer functions to absorbmoisture from a high humidity side and to discharge moisture to a lowhumidity side and thus effectively performs the moisture permeationfunction. As compared with a polyurethane resin layer having a numerousfine perforations formed by a conventional method such as a wet-systemcoagulation method, a method of dissolving fine soluble particles or afoaming method, the non-porous hydrophilic polyurethane resin layer isfree from clogging of perforations and has superior water proofingproperties. A porous substrate provided with such a hydrophilicpolyurethane resin layer is disclosed, for instance, in JapaneseUnexamined Patent Publications No. 203172/1983 and No. 222840/1983.

To form a hydrophilic polyurethane resin layer, it is common to employ amethod wherein a coating composition composed of a mixture of startingmaterials for a hydrophilic polyurethane resin or a solution ordispersion thereof, is directly or indirectly applied to a poroussubstrate to form a coating layer. The indirect application means amethod wherein a not-completely cured coating layer is formed on areleasable substrate, and the coating layer is then laminated on aporous substrate. In some cases, an adhesive may be employed for suchlamination (see above-mentioned Japanese Unexamined Patent PublicationNo. 203172/1983). Otherwise, a sufficiently cured hydrophilicpolyurethane resin film is firstly prepared, and this film may belaminated on a porous substrate. Such a film may be prepared usually byapplying the above-mentioned coating composition to a releasablesubstrate and then cured. The cured film may be laminated on a poroussubstrate by a method wherein it is peeled off from the releasablesubstrate and then laminated on the porous substrate, or a methodwherein it is laminated on the porous substrate while being stillsupported on the releasable substrate, and then the releasable substrateis removed. For the lamination, the adhesive properties or fusibleproperties of the hydrophilic polyurethane resin itself may be utilized,or a separate adhesive may be employed. The moisture permeability may bemaintained by employing, as the adhesive, a moisture permeable adhesive(the moisture permeability may be improved particularly when theadhesive layer is made thin), or by applying the adhesive partially (forinstance, in a pattern of dots or lines).

The hydrophilic polyurethane resin is usually prepared by reacting ahighly hydrophilic polyol with a polyisocyanate compound, as the majorstarting materials. In many cases, a two-component type coatingcomposition is employed which is a combination of an isocyanategroup-containing prepolymer obtained by reacting the highly hydrophilicpolyol with the polyisocyanate compound, and a curing agent for theprepolymer. As the curing agent, a polyfunctional active hydrogencompound having a low molecular weight, such as a diol or a diamine maybe employed. Further, it is also possible to combine a hydroxylgroup-containing prepolymer obtained by reacting a highly hydrophilicpolyol with a polyisocyanate compound, and a curing agent such as apolyisocyanate compound. Furthermore, other than such combinations ofthe prepolymers with the curing agents, it is also possible to prepare acoating composition composed of a mixture of starting materials by aso-called one shot method without preliminarily preparing a prepolymer.If necessary, a compound obtained by blocking, with a blocking agent,isocyanate groups of the isocyanate group containing-prepolymer or ofthe polyisocyanate compound in the above-mentioned methods, may be mixedwith other starting materials to obtain a coating composition ofone-component type.

As mentioned above, the hydrophilic polyurethane resin is obtained froma highly hydrophilic polyol and a polyisocyanate compound as the majorstarting materials. It has been common to employ polyoxyethylene glycolas the highly hydrophilic polyol. However, the use of polyoxyethyleneglycol has various problems. Firstly, when a high moisture permeabilityis desired, no adequate performance is obtainable by a hydrophilicpolyurethane resin prepared by using such a conventional polyoxyethyleneglycol. Namely, the moisture permeability of such a hydrophilicpolyurethane resin is limited, and it is difficult to attain a highermoisture permeability. Secondly, at the time of curing, e.g. when theisocyanate group-containing prepolymer is cured by a curing agent, thecuring rate is very slow, and it is difficult to apply and cure it at arelatively high speed, thus leading to practical and economicalproblems. Thirdly, the isocyanate group-containing prepolymer obtainedby using polyoxyethylene glycol, is solid or liquid with very highviscosity at room temperature, and its handling is cumbersome orinconvenient. Usually, such a prepolymer is employed by dissolving it ina solvent. However, the use of a solvent is likely to bring aboutenvironmental hygienic or economical problems. Therefore, it has beendesired to reduce the amount of the solvent, or to develop a coatingcomposition substantially free from a solvent. Fourthly, the mechanicalproperties of the polyurethane resin obtained by using polyoxyethyleneglycol are not necessarily satisfactory. With the conventionalpolyurethane resin, it is possible to obtain a flexible and highlystretchable coating layer or film, but the mechanical strength is poor.Thus, the conventional product is not satisfactory when a coating layeror film is required to have high mechanical strength while maintainingthe flexibility and stretchability to some extent.

It is an object of the present invention to provide a coatingcomposition for forming a coating layer or film of a hydrophilicpolyurethane resin free from the above-mentioned problems.

The present invention provides a coating composition for forming asubstantially non-porous moisture-permeable coating layer or film of ahydrophilic polyurethane resin, which comprises a polyol combination anda polyisocyanate compound, or a prepolymer or polyurethane resinobtained by reacting them, said polyol combination comprising:

(a) from about 50 to about 98% by weight of a polyoxyethylene polyolhaving an oxyethylene group content of from about 50 to about 90% byweight, a hydroxyl value of from about 15 to about 60 and at least 3hydroxyl groups; and

(b) from about 2 to about 50% by weight of a diol having a molecularweight of from about 62 to about 2,000 which may contain oxyethylenegroups;

provided that the molar equivalent ratio of the component (b) to thecomponent (a) is from about 0.2 to about 5, and the total oxyethylenegroup content in the components (a) and (b) is at least about 70% byweight.

Now, the present invention will be described in detail with reference tothe preferred embodiments.

The coating composition of the present invention may be a so-called oneshot-type composition wherein no prepolymer as mentioned above isemployed, or a composition containing a polyurethane resin. However, itis preferably a composition containing a prepolymer obtained bypreliminarily reacting a polyol component with a polyisocyanatecompound. As mentioned above, the prepolymer includes two types.Preferably, an isocyanate group-containing prepolymer is employed. Forthe coating composition containing a prepolymer, it is necessary to usea curing agent to cure the prepolymer. As the curing agent for anisocyanate group-containing prepolymer, a compound having at least twofunctional groups containing active hydrogen, which are capable of beingreacted with isocyanate groups, such as a polyol, a polyamine, apolythiol or a polycarboxylic acid, may be employed. The polyol as thecuring agent may be the same compound as the polyol in the polyolmixture of the present invention. However, in the present invention,these are regarded as separate components. In the case of one-shot type,the two may not be distinguishable from one another. However, whenpolyols other than the polyoxyethylene polyol (a) and the diol (b) areemployed, they are regarded as the curing agents. Therefore, in the caseof a one-shot method, the use of a curing agent is not essential (as apart of polyols such as the diol (b) is used as a curing agent).Whereas, the curing agent for a prepolymer containing hydroxyl groups,is a compound containing at least two isocyanate groups, such as apolyisocyanate compound. This curing agent may be an isocyanategroup-containing prepolymer. In such a case, the polyol mixture of thepresent invention is divided for the preparation of the respectiveprepolymers. Further, as mentioned above, the polyisocyanate compound orthe isocyanate group-containing prepolymer, may be blocked with ablocking agent. The blocking agent is removed by e.g. heating, whereuponisocyanate groups are freed for reaction. Further, the polyol mixture ofthe present invention does not necessarily mean a polyol compositioncomprising both polyols (a) and (b), and the two types of polyols may beseparately used for the preparation of the respective prepolymers, whichare then mixed. Of course, it is common to employ both polyols (a) and(b) as a mixture. Hereinafter, the coating composition of the presentinvention will be described primarily with respect to a coating materialcomprising an isocyanate group-containing prepolymer obtained byreacting a polyol composition composed of a mixture of both polyols (a)and (b), with a stoichiometrically excess amount of polyisocyanatecompound, and a curing agent for the prepolymer. However, as mentionedabove, the present invention is not restricted to such a specificembodiment.

In the present invention, the polyoxyethylene polyol (a) is obtainableby adding ethylene oxide alone or together with other monoepoxides, to atri- or higher functional initiator. The tri- or higher functionalinitiator is a compound containing functional groups such as hydroxylgroups, amino groups, imino groups or carboxyl groups, to which anepoxide can be added by an addition reaction, and the number of hydrogenatoms in the functional groups is at least 3. Namely, for instance, ahydroxyl group is a monofunctional group, an amino group (--NH₂) is abifunctional group, and an imino group (>NH) is a monofunctional group.A compound having a total of such groups being at least trifunctional,preferably tri- or tetrafunctional, is used as the initiator.Preferably, a tri- or higher functional compound such as a polyhydricalcohol, a polyhydric phenol, an alkanolamine or a polyamine, isemployed. Specifically, the initiator includes glycerol,trimethylolpropane, hexanetriol, pentaerythritol, diglycerol, dextrose,sucrose, diethanolamine, triethanolamine, ethylenediamine,propylenediamine, diaminotoluene and diaminodiphenylmethane. Theseinitiators may be used alone or in combination as a mixture of two ormore. A particularly preferred initiator is a trihydric alcohol such asglycerol or trimethylolpropane.

As the monoepoxide other than ethylene oxide, an alkylene oxide havingat least 3 carbon atoms such as propylene oxide or butylene oxide, ispreferred. However, other epoxides may be used alone or together withthe alkylene oxides. For instance, styrene oxide, epichlorohydrin or aglycidylalkyl (or aryl) ether may be employed. A particularly preferredmonoepoxide other than ethylene oxide is propylene oxide. The manner forthe addition of ethylene oxide and propylene oxide or the like to theinitiator is not particularly limited, and they may be added in a blockform or in a random form.

The polyoxyethylene polyol (a) is required to contain from about 50 toabout 90% by weight of oxyethylene groups. Constituents other thanoxyethylene groups comprise residues of the initiator, or such residuesand residues derived from monoepoxides other than ethylene oxide.Preferably, the polyol (a) contains at least 5% by weight of theresidues of monoepoxides other than ethylene oxide, preferably C₃ -C₄alkylene oxide residues. A polyoxyalkylene polyol wherein theoxyalkylene groups are composed solely of oxyethylene groups, usuallytends to be solid and difficult to handle. Further, it is likely tocause the solidification or high viscosity of the prepolymer describedhereinafter. More preferably, the polyoxyethylene polyol (a) contains atleast about 8% by weight of monoepoxide residues other than theoxyethylene groups, particularly propylene oxide residues (namely,oxypropylene groups). Such a polyoxyethylene polyol having e.g.oxypropylene groups, is usually liquid at room temperature and easy tohandle, and the prepolymer will have a low viscosity. Oxyethylene groupsin the polyoxyethylene polyol (a) are groups which bring abouthydrophilic properties to the polyurethane resin. If the content is toolow, the hydrophilic properties tend to deteriorate. The lower limit ofthe preferred oxyethylene group-content is about 60% by weight, morepreferably about 70% by weight.

The hydroxyl value of the polyethylene polyol (a) is required to be fromabout 15 to about 60. If the hydroxyl value is higher than this range,the flexibility or the texture of the polyurethane resin tends todeteriorate, and at the same time, a hard block of the polyurethaneresin having poor hydrophilic properties tends to increasecorrespondingly, whereby the hydrophilic properties tend to deteriorate.On the other hand, if the hydroxyl value is lower than the above range,the viscosity of the prepolymer increases, and the reaction rate of theprepolymer with the curing agent, tends to be low. Further, thehydrophilic properties of the polyoxyethylene polyol (a) tend to bepoor, thus leading to a deterioration of the hydrophilic properties ofthe polyurethane resin. The upper limit of the preferred hydroxyl valueof the polyoxyethylene polyol (a) is about 50, and the lower limit isabout 20, more preferably about 25.

As the diol (b), various diols such as a dihydric alcohol, apolyoxyalkylene diol and a polyester diol, may be employed. However, aswill be described later, this diol (b) should not be the one whichhinders the hydrophilic properties of the polyurethane resin.Accordingly, when a diol having a relatively high molecular weight isused, the amount (weight amount) increases, and the diol must be highlyhydrophilic. On the other hand, in the case of a diol having arelatively low molecular weight, the amount (weight amount) is small,and it is possible to employ a diol having relatively low hydrophilicnature. The hydrophilic properties are governed mainly by the proportionof oxyethylene groups contained in the polyoxyethylene polyol (a) andthe diol (b) relative to the total weight of the polyol (a) and diol(b). The oxyethylene group content is at least about 70% by weight,preferably at least about 75% by weight. The upper limit is usuallyabout 95% by weight. In the present invention, ethylene glycol,diethylene glycol and a polyoxyethylene glycol having a higher degree ofpolymerization, are regarded to have an oxyethylene group content of100% by weight. Thus, so long as the total oxyethylene group content inthe polyoxyethylene polyol (a) and the diol (b) constituting the polyolmixture of the present invention, is within the above-mentioned range,the oxyethylene group content in the diol (b) has no particularlimitation, and the diol (b) may not contain oxyethylene groups at all.As shown by the molar ratio described hereinafter, a diol (b) having arelatively high molecular weight should preferably be a polyoxyethylenediol having a high content of oxyethylene groups since the amount(weight amount) increases. Contrary, a diol (b) having a relatively lowmolecular weight is used in a small amount (weight amount), andaccordingly, it may be a polyhydric alcohol, a polyether diol orpolyester diol, which contains no oxyethylene groups, such as1,4-butanediol, neopentyl glycol, dipropylene glycol, and other lowmolecular weight polyoxypropylene diols, and low moelcular weightpolyester diols. For the same reason, when the oxyethylene group contentin the polyoxyethylene polyol (a), is higher, it is possible to use adiol (b) having a less content of oxyethylene groups. As a diol (b)having a relatively high molecular weight, it is preferred to employ, inaddition to polyoxyethylene glycol, a polyoxyethylene diol obtainable byadding ethylene oxide, or ethylene oxide and other monoepoxides(particularly alkylene oxides) to a various bifunctional initiator (suchas a dihydric alcohol or a dihydric phenol). This polyoxyethylene diolhas the same structure as the above-mentioned polyoxyethylene polyol (a)except that it is bifunctional, and may be prepared by using the samematerial and method except that a bifunctional initiator is employed.

The molecular weight of the diol (b) is from about 62 to about 2000. Thelower limit of this molecular weight is the molecular weight of ethyleneglycol i.e. a diol having the lowest molecular weight. A diol having amolecular weight exceeding about 2000, tends to have a high oxyethylenegroup content as mentioned above, and as a result, the viscosity of theprepolymer increases. The upper limit of the molecular weight of apreferred diol (b) is about 1500, more preferably about 1200. It ispreferred that the oxyethylene group content of a diol (b) having amolecular weight of at least about 400 is at least about 30% by weight,and the oxyethylene group content of a diol having a molecular weight ofat least about 800, is at least about 60% by weight, although theoxyethylene group content is not so restricted. Most preferably, apolyoxyethylene glycol having a molecular weight of at least about 800,especially at least about 300, is used.

The coating composition of the present invention is preferably the onewhich is capable of providing a coating layer or film having not onlyhigh moisture-permeability but also high levels of elongation andtensile strength. For this purpose, the diol (b) is preferably a diolhaving a relatively high molecular weight. Thus, a preferred diol (b)has a molecular weight of from about 300 to about 1500. This diol havinga relatively high molecular weight is required to have a highoxyethylene group content as mentioned above. The oxyethylene groupcontent within the above-mentioned relatively low molecular weightrange, is preferably at least about 30% by weight, more preferably atleast about 60% by weight. A particularly preferred oxyethylene groupcontent of the diol having a relatively high molecular weight is fromabout 60 to about 100% by weight. Most preferably, a polyoxyethyleneglycol wherein substantially all the oxyalkylene groups are oxyethylenegroups, is employed.

Each of the polyoxyethylene polyol (a) and the diol (b) may be acombination of two or more different kinds. For instance, as the polyol(a), a mixture of a triol and tetrol, or a mixture of polyols havingdifferent molecular weights, may be employed. It is usual to employ apolyoxyethylene polyol (a) and a diol (b) which are separately prepared.However, in some cases, their mixture may be prepared and employed. Forinstance, a mixture comprising a polyoxyethylene polyol (a) and a diol(b) can be obtained by adding e.g. ethylene oxide to a mixturecomprising a tri-functional initiator or polyether polyol (having amolecular weight lower than the desired molecular weight) and abifunctional initiator or polyether diol (having a molecular weightlower than the desired molecular weight). When the proportion of the twoare outside the proportions described hereinafter, a deficient (a) or(b) may be supplemented to such a mixture.

The polyol mixture of the present invention comprises from about 50 toabout 98% by weight of the polyoxyethylene polyol (a) and from about 2to about 50% by weight of the diol (b). As mentioned above, this weightratio may be varied within a wide range depending upon the molecularweight of the diol (b). Accordingly, the ratio of the two is preferablyprimarily defined by the molar ratio. Namely, in the present invention,the molar equivalent ratio of the diol (b) to the polyoxyethylene polyol(a) is from about 0.2 to 5. A preferred molar equivalent ratio of thediol (b) is from about 0.3 to about 3, particularly preferred is fromabout 0.4 to about 2. Normally, it is preferred that the higher themolecular weight of the diol (b), the higher the molar equivalent ratiobecomes.

As mentioned above, it is preferred that the polyol mixture is reactedwith a stoichiometrically excess amount of the polyisocyanate compoundto obtain an isocyanate group-containing prepolymer, which is thenblended to a coating composition. The isocyanate group-containingprepolymer is prepared usually by reacting the polyol mixture and thepolyisocyanate compound under heating optionally in the presence of asolvent or a catalyst for the formation of urethane. The amount of thepolyisocyanate compound is preferably determined by the isocyanate groupcontent in the resulting prepolymer, since the composition of the polyolmixture may vary to a large extent as mentioned above. The isocyanategroup content in the isocyanate group-containing prepolymer ispreferably from about 3 to about 15% by weight, more preferably fromabout 3 to about 8% by weight. In the present invention, the viscosityof the isocyanate group-containing prepolymer is substantially low ascompared with a similar prepolymer prepared by using a conventionalpolyoxyethylene glycol. An isocyanate group-containing prepolymerobtained by using a polyoxyethylene glycol having a molecular weight ofabout 2000 as a typical polyoxyethylene glycol, is solid at roomtemperature. Whereas, the isocyanate group-containing prepolymer in thepresent invention, is usually liquid at room temperature, and even if itis solid, its melting point is substantially lower than the meltingpoint of the conventional product. Preferably, the prepolymer of thepresent invention has a viscosity of at most about 20,000 centipoise,more preferably at most about 10,000 centipoise, as measured at 25° C.Such a low viscosity prepolymer can be made into a coating compositionwhich can be coated without using any solvent.

Various compounds having at least two isocyanate groups may be employedas the polyisocyanate compound. For instance, there may be mentioned anaromatic polyisocyanate, an aliphatic polyisocyanate, an alicyclicpolyisocyanate, and modified products thereof. Further, such compoundsmay be employed in combination as a mixture of two or more differenttypes. Preferably, an aromatic polyisocyanate is used. When anon-yellowing property is required, a non-yellowing modified aromaticpolyisocyanate or non-aromatic polyisocyanate may be employed. Specificyellowing aromatic polyisocyanates include tolylene diisocyanate,diphenylmethane diisocyanate, polymethylenepolyphenyl isocyanate,tolidine diisocyanate, naphthalene diisocyanate and triphenylmethanetriisocyanate. Non-yellowing aromatic polyisocyanates include xylenediisocyanate and α,α,α',α'-tetramethylxylylene diisocyanate. Aliphaticpolyisocyanates include hexamethylene diisocyanate and lysinediisocyanate. Aliphatic polyisocyanates include isophorone diisocyanate,dicyclohexylmethane diisocyanate and bis(isocyanatomethyl)cyclohexane.Modified products include a prepolymer-type modified product obtained bymodifying with a polyhydric alcohol such as trimethylolpropane, acarbodiimide-modified product, a urea-modified product, a dimer and atrimer. As the polyisocyanate compound, a bifunctional compound issubstantially preferred. Particularly preferred is an aromaticdiisocyanate.

For the curing of the above-mentioned isocyanate group-containingprepolymer, a curing agent is required. As mentioned above, a compoundhaving at least two active hydrogen-containing functional groups is usedas the curing agent. Particularly, a relatively low molecular weightpolyol, alkanolamine or polyamine, is preferably employed. Particularlypreferred curing agents are diols or diamines having a molecular weightof at most about 300, especially at most about 200. For instance,ethylene glycol, 1,4-butanediol, neopentyl glycol, 1,6-hexanediol,ethylenediamine, tetramethylenediamine, hexamethylenediamine,dichlorobenzidine and isophoronediamine are preferred. It is alsopossible to use water as a curing agent. However, water is not usuallyemployed because it may cause foaming, whereby the coating layer tendsto be porous. In some cases, it is possible that no curing agent isincorporated in the coating composition, and the coated prepolymer iscured by moisture in the air or by a polyamine vapour. The curing agentis used preferably in an amount of from about 0.5 to about 1.3 mols,more preferably from about 0.6 to about 1.1 mols per mole of theisocyanate group-containing prepolymer.

Various components other than the above-mentioned major materials i.e.other than the polyol mixture and the polyisocyanate compound, or theprepolymer and its curing agent, may also be incorporated to the coatingcomposition of the present invention. As one of such optionalcomponents, a solvent may be mentioned. Particularly when a prepolymerhaving a high viscosity is employed, it is preferred to use a solvent.However, when the viscosity of the prepolymer is not higher than about10,000 centipoise (at 25° C.), the coating composition may be madesubstantially solventless. Another optional component is a stabilizer.For instance, various stabilizers which are commonly called ultravioletabsorbers, photostabilizers or antioxidants, may be incorporated.Further, a urethane-forming catalyst such as a tertiary amine or anorganic tin compound may be incorporated to facilitate the curingreaction. Furthermore, a flame retardant, a filler, a coloring agent, aplasticizer or any other optional components, may be incorporated.

The coating composition of the present invention may be applied to andcured on a porous substrate or a releasable substrate to obtain acoating layer or a film. The coating layer or the film thereby obtainedshould be substantially non-porous. Accordingly, a curing method forforming a porous film such as a wet coagulation method is not employed.The coating layer or film obtained by the coating composition of thepresent invention may be in the form of a foam having independent cells.Namely, it may be a coating layer or film in the form of a foam havingno substantial gas permeability. However, the coating layer or filmobtained from the coating composition of the present invention ispreferably a substantially foamless coating layer or film i.e. asubstantially solid coating layer or film.

Now, the present invention will be described in further detail withreference to Examples. However, it should be understood that the presentinvention is by no means restricted to these specific Examples.

EXAMPLE 1

Tolylene diisocyanate (a mixture of 2,4-form/2,6-form in a weight ratioof 80/20) was reacted at 90° C. for 4 hours, to a mixture comprising 770parts (parts by weight, the same applies hereinafter) of a triol havinga hydroxyl value of 48.1 obtained by adding a mixture of ethyleneoxide/propylene oxide (weight ratio of 80/20) to glycerol and 20 partsof diethylene glycol, to obtain an isocyanate group-containingprepolymer having an isocyanate group content of 5.9% by weight. Theviscosity of this prepolymer was 6500 cp (centipoise) as measured at 25°C. (the same applies hereinafter), and the prepolymer was liquid at roomtemperature.

To 200 parts of the above prepolymer, 7.25 parts of ethylene glycol [theratio of isocyanate groups/hydroxyl groups in number (hereinafterreferred to as NCO/OH) being 1.2] was added and mixed, and the mixturewas coated in a thickness of 0.05 mm on the surface of a releasablepaper sheet, then laminated to a 70 denier nylon taffeta, and cured in aconstant temperature chamber of 100° C. for 3 hours. Then, thereleasable paper was peeled off. The obtained cloth was subjected to themeasurement of moisture permeability in accordance with JIS (JapaneseIndustrial Standard) Z-0208.

On the other hand, the same prepolymer and ethylene glycol were mixed inthe same proportions, and the mixture was coated in a thickness of 0.2mm on the surface of a releasable paper sheet, and then cured in thesame manner as described above to obtain a film having a thickness of0.2 mm. By using this film, the mechanical properties were measured inaccordance with JIS K-6301.

Furthermore, the same prepolymer and ethylene glycol were mixed in thesame proportions, and the time until the mixture turned into a gel at100° C. (hereinafter referred to as the "gelation time") was measured.

The results of these tests are shown in Table 1.

EXAMPLE 2

To a mixture comprising 662 parts of the same triol having a hydroxylvalue of 48.1 as used in Example 1 and 117 parts of a polyoxyethyleneglycol having a molecular weight of 400, 221 parts of tolylenediisocyanate was added, and the mixture was reacted at 90° C. for 4hours to obtain an isocyanate group-containing prepolymer having anisocyanate group content of 5.8% by weight and a viscosity of 7000 cp.

By using this prepolymer and ethylene glycol in an amount such that theratio of NCO/OH in number would be 1.2, the moisture permeability, themechanical properties and the gelation time were measured in the samemanners as in Example 1. The results are shown in Table 1.

EXAMPLE 3

To a mixture comprising 472 parts of the same triol having a hydroxylvalue of 48.1 as used in Example 1 and 314 parts of a diol having ahydroxyl value of 113 obtained by adding a mixture of ethyleneoxide/propylene oxide (weight ratio of 80/20) to propylene glycol, 214parts of tolylene diisocyanate was added, and the mixture was reacted at90° C. for 4 hours to obtain an isocyanate group-containing prepolymerhaving an isocyanate group content of 5.9% by weight and a viscosity of4900 cp.

By using this prepolymer and ethylene glycol in an amount such that theNCO/OH ratio would be 1.2, the same tests as in Example 1 wereconducted. The results are shown in Table 1.

EXAMPLE 4

To a mixture comprising 732 parts of the same triol having a hydroxylvalue of 48.1 as used in Example 1 and 31 parts of 1,4-butanediol, 238parts of tolylene diisocyanate was added, and the mixture was reacted at90° C. for 4 hours to obtain an isocyanate group-containing prepolymerhaving an isocyanate group content of 6.0% by weight and a viscosity of6200 cp.

By using this prepolymer and ethylene glycol in an amount such that theNCO/OH ratio would be 1.2, the same tests as in Example 1 wereconducted. The results are shown in Table 1.

EXAMPLE 5

To a mixture comprising 600 parts of a triol having a hydroxyl value of28.1 obtained by adding a mixture of ethylene oxide/propylene oxide(weight ratio of 70/30) to trimethylolpropane and 400 parts of apolyoxyethylene glycol having a molecular weight of 1000, 230 parts ofxylylene diisocyanate was added, and the mixture was reacted at 90° C.for 6 hours to obtain an isocyanate group-containing prepolymer havingan isocyanate group content of 5.2% by weight and a viscosity of 9200cp.

By using this prepolymer and ethylene glycol in an amount such that theNCO/OH ratio would be 1.2, the same tests as in Example 1 wereconducted. The results are shown in Table 1.

COMPARATIVE EXAMPLE 1

To 820 parts of the same triol having a hydroxyl value of 48.1 as usedin Example 1, 180 parts of tolylene diisocyanate was added, and themixture was reacted at 90° C. for 4 hours to obtain a prepolymer havingan isocyanate content of 5.9% by weight.

By using this prepolymer and ethylene glycol in the same proportions asin Example 1, the same tests as in Example 1 were conducted. Theviscosity of the prepolymer and the test results are shown in Table 1.

COMPARATIVE EXAMPLE 2

793 parts of a polyoxyethylene glycol having a molecular weight of 2000and 207 parts of tolylene diisocyanate, were reacted at 90° C. for 4hours to obtain a prepolymer having an isocyanate group content of 6.6%by weight which was solid at room temperature.

This prepolymer was mixed at 60° C. with ethylene glycol in the sameproportion as in Example 1, and the mixture was subjected to the sametests as in Example 1. The results are shown in Table 1.

COMPARATIVE EXAMPLE 3

740 parts of a triol having a hydroxyl value of 112.2 obtained by addingonly ethylene oxide to trimethylolpropane, and 260 parts of tolylenediisocyanate, were reacted at 90° C. for 4 hours to obtain a prepolymerhaving an isocyanate group content of 6.2% by weight.

By using this prepolymer and ethylene glycol in the same proportion asin Example 1, the same tests as in Example 1 were conducted. The resultsare shown in Table 1.

COMPARATIVE EXAMPLE 4

To a mixture comprising 248 parts of the same triol having a hydroxylvalue of 48.1 as used in Example 1 and 579 parts of a polyoxyethyleneglycol having a molecular weight of 2000, 173 parts of tolylenediisocyanate was added, and the mixture was reacted at 90° C. for 5hours to obtain an isocyanate group-containing prepolymer having anisocyanate group content of 4.8% by weight and a viscosity of 17,500 cp.

By using this prepolymer and ethylene glycol in an amount such that theNCO/OH ratio would be 1.2, the same tests as in Example 1 wereconducted. The results are shown in Table 1.

                                      TABLE 1                                     __________________________________________________________________________           Viscosity of                                                                        Gelation                                                                           Moisture-   Elongation                                                                          Tensile                                                                            Tear                                        prepolymer                                                                          time permeability                                                                              (0.2 mm)                                                                            strength                                                                           strength                                    [cp]  [min]                                                                              [g/m.sup.2 · 24 hr · 0.05                                               [%]   [kg/cm.sup.2 ]                                                                     [kg/cm]                              __________________________________________________________________________    Example 1                                                                            6,500 29   7,200       100   32   25                                   Example 2                                                                            7,000 32   7,000       206   52   26                                   Example 3                                                                            4,900 35   7,800       316   66   28                                   Example 4                                                                            6,200 30   7,200       143   45   26                                   Example 5                                                                            9,200 51   7,900       350   64   29                                   Comparative                                                                          6,200 27   6,200        43   15   19                                   Example 1                                                                     Comparative                                                                          Solid 135  5,400       280   20   15                                   Example 2                                                                     Comparative                                                                          68,000                                                                              23   3,200        32   23   21                                   Example 3                                                                     Comparative                                                                          17,500                                                                              104  5,700       490   47   33                                   Example 4                                                                     __________________________________________________________________________

The coating composition of the present invention makes it possible toproduce a highly moisture-permeable coating layer or film, and at thesame time, it has a high curing rate and thus can practicallyadavantageously be used. Further, the prepolymer has a low viscosity,and it is possible to obtain a coating composition containing nosolvent, which is advantageous not only from the viewpoint of theenvironment hygiene but also from the viewpoint of economy since theenergy cost for the curing is minimum. Furthermore, the composition ofthe present invention has a feature that the balance of the elongationand other mechanical properties can be varied, and it is possible toobtain e.g. a highly strong film or a laminated cloth having anexcellent texture.

We claim:
 1. A coating composition for forming a substantiallynon-porous moisture-permeable coating layer or film of a hydrophilicpolyurethane resin, which comprises (i) a prepolymer of a polyolcombination and a polyisocyanate compound, said prepolymer having aviscosity of a most 10,000 cp at 25° C. and (ii) a curing agent for saidprepolymer selected from the group consisting of a diol and a diaminehaving a molecular weight of 200 or less, said polyol combinationcomprising:(a) from about 50 to about 98% by weight of polyoxyethylenepolyol having an oxyethylene group content of from about 50 to about 90%by weight, at least 5% by weight of C₃ -C₄ alkylene oxide residues, ahydroxyl value of from about 15 to about 60 and at least 3 hydroxylgroups; and (b) from about 2 to about 50% by weight of a diol having amolecular weight of from about 62 to about 2,000 which may containoxyethylene groups; provided that the molar equivalent ratio of thecomponent (b) to the component (a) is from about 0.3 to about 3, and thetotal oxyethylene group content in the components (a) and (b) is fromabout 75% to about 95% by weight.
 2. The composition according to claim1, which comprises isocyanate groupcontaining prepolymer obtained byreacting the mixture of the polyoxyethylene polyol (a) and the diol (b)with a stoichiometrically excess amount of the polyisocyanate compound.3. The composition according to claim 2, wherein the isocyanategroup-containing prepolymer contains from about 3 to about 15% by weightof isocyanate groups.
 4. The composition according to claim 1, whereinthe polyoxyethylene polyol (a) is an adduct obtained by adding ethyleneoxide alone or together with other monoepoxides to a tri- or higherfunctional initiator selected from the group consisting of a polyhydricalcohol, a polyhydric phenol, an alkanolamine, a polyamine, and amixture thereof.
 5. The composition according to claim 4, wherein theinitiator is glycerol, trimethylolpropane, hexanetriol, pentaerythritol,diglycerol, dextrose, sucrose, diethanolamine, triethanolamine,ethylenediamine, propylenediamine, diaminotoluene,diaminodiphenylmethane or a mixture thereof.
 6. The compositionaccording to claim 1, wherein the diol (b) is a dihydric alcohol, apolyoxyalkylene diol, a polyester diol or a mixture thereof.
 7. Thecomposition according to claim 6, wherein the diol (b) is apolyoxyethylene diol having a molecular weight of from 300 to 1500 andan oxyethylene group content of at least 60% by weight.